How to polish fused silica to obtain the surface damage threshold equals to the bulk damage threshold

We compared the 1064 nm surface damage thresholds of fused silica polished by three different techniques: 1. A conventional polishing technique: that uses loose Alumina abrasives (lapping) followed by a fine Cerium oxide polish. 2. An alumina polishing process producing surfaces very close to super polished. 3. Process 2 followed by a silica polish until the silica surfaces are super polished. We employed the same measurement technique that proved successful for the bulk damage threshold measurement to measure the damage thresholds of bare silica surfaces polished by the above three polishing techniques. We used an 8-nanosecond, single transverse and longitudinal mode pulsed laser, from a Q-switched Nd:YAG laser. We used the surface third harmonic generation technique to precisely place the focus of the laser beam on the surface of the fused silica window, and to measure the laser focus spot size which was found to be 8 μm in radius.